A coroner has concluded the risk of sudden death in babies is higher if they sleep with their parents.

An inquest in Adelaide investigated the deaths of five babies ranging from three weeks to 10 months old.

Causes of death were undetermined but autopsy results indicated the infants may have suffocated.

In four of the five cases the babies had slept with a parent or grandparent.

In one case a father had tried to settle his daughter while on a sofa but fell asleep.

He woke and found her unresponsive between a pillow and the back of the sofa.

Naomi Kade was 10 months old when she died in July 2007 and Jaia Denise Nelson was just three weeks old when she died the following month.

James Samuel Cleland was four months old when he died in September 2008 and Diesel Jay Phelan, three months, and Hannah Nicole Francis, one month old, both died in November that year.

In two of the cases a mother and a grandmother who slept with babies had been under the influence of alcohol and medication respectively.

The inquest heard such factors further increased the risk of sudden infant death during co-sleeping.

South Australian Coroner Mark Johns concluded that the risk of sudden death rose when babies slept with adults.

"The message to be drawn from these five tragic deaths is that the risk of sudden, unexplained death in infancy is greatly increased where a child sleeps in the same bed with one or more parents or other adults, whether the mechanism of death is asphyxia due to overlaying, bedding or otherwise," he concluded.

"On the other hand, there are benefits to parents sharing a room with an infant where the infant is sleeping in a safe cot expressly designed for that purpose."

A pathologist with Forensic Science SA, Professor Roger Byard, had told the inquest that parents needed to put an emphasis on room sharing rather than bed sharing.

He said an infant should sleep in a cot near the parents' bed.

"Certain infants taken into the parental bed will not survive the night," he said.